1. Field of the Invention
This invention relates to clutch discs having vibration damping means and particularly to clutch discs having a drive disc attached to a hub with intermediate rings and support rings on each side of the drive disc and with damping rings between the hub and each intermediate ring and between each intermediate ring and the respective support ring to provide a structure in which the damping rings may be properly pre-stressed.
2. The Prior Art
German OS No. 14 25 260 describes a vibration damping clutch disc suitable for a motor vehicle and including a hub with a drive disc, damper rings of elastomeric material connected to the hub on each side of the drive disc and vulcanized to the generally cylindrical inner surfaces of intermediate rings, and additional damping rings vulcanized directly to the outer surfaces of the respective intermediate rings and connected to outer support rings, respectively. The support rings are connected to each other and to a friction disc by a connecting element, and the connecting element, as well as bosses of the intermediate rings, face each other in the axial direction and engage in cutouts of the drive disc. The intermediate rings have several projections distributed over their respective circumferences, and these projections, in conjunction with stops of the drive disc associated with these projections, limit the relative twisting mobility of the structure.
The stability of the relationship of the intermediate rings and the hubs of the structure just described is very low. From different degrees of loading of the individual stops, which can result from insufficient mutual matching of the dimensional tolerances of the parts, radial displacement of the intermediate rings and, therefore, of the friction disc from the axis of rotation can occur. Such radial displacement is extremely undesirable, and in order to reduce it, elastic pre-tension of the damper rings by a mutual connection of the support rings was proposed. The magnitude of this pre-tension is the same in all damper rings but specifically only if the receiving cross-sections are identical. The radially inner damper rings, therefore, have a greatly enlarged cross-section, which increases the weight of the clutch disc, and is therefore undesirable. The same feature also results in a relatively steep slope of the spring characteristic when small torques are transmitted, and this feature is also undesirable.
The purpose of vibration-damping is to isolate vibrations generated by the engine when it is idling or when it is transmitting small torques, and to damp vibrations generated when nominal torque is transmitted. Starting shocks and other overloads are also to be intercepted.
For the lower torque range, a flat spring characteristic is required, which is not necessary in the upper torque range In addition to the disadvantages discussed hereinabove, the prior clutch disc does not satisfactorily fulfill this basic requirement.